High Capacity Multi-Lithium Oxide Cathodes and Oxygen Stability

Jagjit Nanda Email: [email protected] Phone: 865- 241-8361

Oak Ridge National Laboratory

2018 U.S. DOE Vehicle Technologies Office Annual Merit Review

June 19, 2018 Project ID: BAT106

This presentation does not contain any proprietary, confidential, or otherwise restricted information

ORNL is managed by UT-Battelle for the US Department of Energy Overview Timeline Barriers

• Project start date: Oct. 1, 2015 Performance: High energy density for • Project end date: Sept. 30, 2018 PEV applications with cell level targets ≥ • Percent complete: 100% 400 Wh/kg and 750 Wh/L Life: 2000 deep discharges (SoC range) over the entire life Safety: Thermally stable and abuse tolerant

Budget Partners/Collaborators

• FY17 Funding: $ 400K • Pacific Northwest National Laboratory • FY18 Funding: $ 400K Electron Microscopy • Brookhaven National Laboratory Synchrotron X-ray diffraction • Lawrence Berkeley National Laboratory Modelling and insitu DEMS

2 Relevance Objectives :

(I) Develop high-voltage and high-capacity cathode materials for lithium-ion batteries to achieve Battery 500 goal of 500 Wh/kg for 1000 cycles.

(II) Recent studies have shown specific rock salt disorder lithium excess oxides enable high voltage stability with either minimal oxygen loss or reversible oxygen redox with no irreversible structural transformation.

(III) Most of the disordered oxides studied in this project belong to early transition metal (TM) group such as Mo, Cr, Ti with no cobalt.

Cation disorder & lithium excess Composition guided from modeling

Anionic/oxidative stability Electrochemical Interfacial & performance structural stability Li storage properties Utilize cation-disorder as a means to optimize and stabilize high voltage cathodes

3 Milestones Due Date Description Status

06/30/2017 Synthesize one particular class and composition of cation Complete (Q3) disordered cathodes: Li2MoO3 and Cr - substituted Li2MoO3

Complete structural and electrochemical performance analysis of 09/30/2017 disordered cathodes - Li MoO and Cr substituted Li MoO (No- Complete (Q4) 2 3 2 3 Go) Revised to include Cr doped NMC and MoO3 coated NMC Complete neutron powder diffraction, microstructural analysis and gas evolution studies of Li MoO cathodes synthesized using 12/31/2017 2 3 solid state/sol-gel method as well as sputtered thin film Complete (Q1) electrodes with no binders and carbon. Evaluate and analyze oxygen stability between 4.3-4.8 V

Synthesis and electrochemical performance testing of at least 03/31/2018 two composition of Mo doped Ni-rich NMC composition. Initially Complete (Q2) Mo doping will be varied between 3-10 %

Synthesize one particular class and composition of disorder composite cathodes with Li MoO as a structural unit for 06/30/2018 2 3 stabilizing the NMC cathodes. Continue looking for stable In progress (Q3) phases with the compositional space xLi2MoO3. (1-x) LiMO2; with x = 0.2 - 0.4 and M = Mn, Ni, Co. Undertake structural and electrochemical performance analysis 09/30/2018 of disorder cathodes of few selected composition of xLi MoO . (1- 2 3 In progress (Q4) x) LiMO2 in order to get a mechanistic understanding of the 4 oxygen stability and the role of disorder Approach/Strategy Design and synthesis of high-voltage, high-capacity lithium excess oxide cathodes guided by state-of-the-art characterization and modeling based on the following approach - Mitigate and address unfavorable irreversible structural transition and oxygen loss in lithium excess TM oxides by effective control of cation mixing (disorder) during delithiation. - In this specific approach substituting early transition metals such as Mo, Cr, and Ti in lithium excess rock salt cathode structures can provide high capacity and oxidative stability. - Oxygen participation in redox process: Oxygen participation, commonly referred to as “anionic redox” could be a viable approach for obtaining high reversible

capacity as reported in Li2Ru0.50Sn0.50O3 and Li1.25Mn0.50Nb0.25O2. - Use in-situ and ex-situ local probe spectroscopy and microscopy to understand coupling between oxygen redox and cation disorder (migration) Disordered, Li-excess Cathode

Delithiation O-(2-δ) species Images adapted with 5 Li Mn Nb O permission from: Seo et al. Li1.25Mn0.5Nb0.25O2 0.25 0.5 0.25 2 Nat. Chem, 2016, 8, 692. Technical Accomplishment

Li2MoO3 was synthesized and characterized as a structural unit that can be integrated to stabilize high voltage cathodes

Li2MoO3 Synthesis Procedure Precursor: Li2MoO4 powder (commercial) Heating: Heat at 675 °C under flowing Ar/H (96/4) 2 Li

XRD (λ = 1.54 Å) MoO6 Octahedral

Li2MoO4 Precursor

675°C, 12 h (Mixed Phase)

675°C, 48 h (Phase Pure Li2MoO3)

JCPDS 84-1782 Neutron Diffraction (λ = 0.7Å) Intensity / A.U. / Intensity Rw = 2.951% 10 20 30 40 50 60 70 80

2θCuKα / deg. Intensity / A.U. A.U. Intensity /

0 1 2 3 4 5 6 7 2 µm d-spacing / Å 6 Self et al., Chemistry of Materials, Under Review With Ashfia Huq, ORNL Technical Accomplishment

(I) Li2MoO3 electrodes are electrochemically active demonstrating up to 1 Li reversible capacity and (II) No significant oxygen evolution up to 4.8 V

Scan 1 In-Situ Mass Spectrometry Scan 2 80

1 Scan 3 -

g Scan 4 40 Gas Li Outlet 0 Auxiliary Electrolyte -40 Oxidation Working

CurrentmA / 4+/5+/6+ Gas Inlet Electrode -80 Mo

2 3 4 5 5 + 1.4 Potential / V vs. Li/Li + Potential O 1.2 4 2 + 5.0 CO2 1.0 4.5 3 0.8 4.0 Cycle1 0.6 3.5 Cycle 5 2 0.4 % / Content Gas Cycle 10 3.0 0.2

Cycle 50 vs. Li/Li V / Potential 2.5 1 0.0

Potential / V vs. Li/Li V / Potential 0 200 400 600 800 1000 1200 2.0 Time / min 0 0.2 0.4 0.6 0.8 1.0 1.2 7 mol Li+ Self et al., Chemistry of Materials, under Review With G. Veith ORNL Technical Accomplishment Synchrotron XRD at different voltage (SoC) shows gradual loss of crystallinity for Li MoO 2-x 3 2.0

+ A003/A104 A /A 5.0 1.5 003 111 (Al) 4.5 Pristine 4.0 1.0 Closed symbols: 1st charge 3.5 Open symbols: 1st discharge 3.0 0.5 Pristine

2.5 Relative Intensity Relative 2.0 0.0

Potential / V vs. Li/Li V / Potential 0 0.2 0.4 0.6 0.8 1.0 1.2 2 3 4 5 mol Li+ transferred Potential / V vs. Li/Li+

(003) (111)Al (104) Normalized Intensity 0

0.12

Discharge Discharge 0.25 0.37

0.50 Charge Charge 3.2 3.4 3.6 3.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2 2θ / deg. (λ = 0.2953 Å) 2θ / deg. (λ = 0.2953 Å)

Collaboration with Feng Wang, 8 Brookhaven National Laboratory Li2-xMoO3 becomes less crystalline during first cycle Technical Accomplishment Combination of techniques show Li2MoO3 becomes mostly amorphous after several cycles. Interestingly, this amorphization does not prevent

reversible Li storage. 1 XRD (220)Al - 300

g Charge 250 10th Cycle (Discharged) Discharge 200 10th Cycle (Charged) 150 100

Pristine 50 Intensity / A.U. / Intensity

Capacity / mAh / Capacity 0 JCPDS 84-1782 0 10 20 30 40 50 Cycle Index 20 30 40 50 60 70 Pristine 1 Cycle 2 Cycles 50 Cycles 2θCuKα / deg. Raman Spectroscopy

10th Cycle (Discharged) 100 nm 200 nm 100 nm 200 nm 10th Cycle * (Charged) * + +

Intensity / A.U. / Intensity * Pristine 250 500 750 1000 Raman Shift / cm-1 Crystalline to Amorphous Transformation * Mo=O vibrational modes Collaboration with Chongmin Wang, Pacific 9 + Mo-O-Mo stretches Northwest National Laboratory Technical Accomplishment Thin film Li2MoO3 cathodes with no binder and carbon black were fabricated using R-F sputtering method for studying the structural changes and the electrode/electrolyte interface

Li2MoO3 sputtering conditions: 60 W, 20 mTorr Ar, 4.9 nm/min (1.01 mm)

Raman Spectroscopy

Li2MoO3 Thin Film

XRD

Li2MoO3 Powder

• Desired thin film structure confirmed via Raman and XRD • Differences in Raman peak intensity attributed to preferential crystallographic orientation of thin film

With A.K. Kercher, ORNL 10 Technical Accomplishment

Ex-Situ Raman and XPS characterization of thin film Li2MoO3 cathodes provides additional insight on charge compensation mechanism

Cycled Thin Film Cathode 1. Band broadening indicates amorphization during cycling Cycled Slurry Cast Cathode 2. Good agreement between thin film and slurry cast cathodes

Pristine Thin Film Counts / A.U. A.U. Counts /

Pristine Li2MoO3 Powder 200 600 1000 1400 XPS Analysis: Mo3d Raman Shift / cm-1 20 Cycles Discharged to 2.0 V 6+ 1. Pristine Li2MoO3 contains significant amount of Mo • Surface layer composed of Li2MoO4 (not detectable by XRD or Raman) 2. Cycled cells contain mixed oxidation states Mo4+/Mo6+ Charged to 4.0 V • Result consistent with formation of disordered glassy

phase Intensity / A.U. Intensity / Pristine Li2MoO3

Sample Mo4+ (at%) Mo6+ (at%) 248 244 240 236 232 228 224 Binding Energy / eV Pristine 0 100 Charged to 4.0V 32.0 68.0 XPS analysis performed by N. Phillips Discharged to 2.0V 67.9 32.1 11 Self et al., Unpublished 2018 Technical Accomplishment

Composite cathodes with the formula 0.15Li2MoO3•0.85LiNi1/3Mn1/3Co1/3O2 were synthesized, and their structure was analyzed using neutron and X-ray diffraction

Synthesis Route High energy ball milling to blend Li2MoO3 + NMC powders followed by firing (850°C)

Ball-Milled Composite (003) Reflection Splitting

ത • NMC and Li2MoO3 have desired R3m symmetry • Composite is two-phase mixture with minor Li3MoO4 impurity phase (~5%)

12 Self et al., Chemistry of Materials, Under Review Technical Accomplishment Electrochemical properties of Mo-NMC composite cathodes with and without heat treatment were compared with NMC

+ 5.5 Unheated Composite: 5.0 • Discharge profile is superposition of endmembers 4.5 4.0 3.5 Heated Composite: 3.0 • Ni3+/4+, Mn3+/4+, and Co3+/4+ are main redox centers 2.5

Potential / V vs. Li/Li V / Potential 2.0 0 50 100 150 200 Capacity / mAh g-1 100

1 250 -

g 80 200 Capacity 60 150 Normalization 40 100 20 50

Capacity / mAh / Capacity 0 0 % / RetentionCapacity 0 5 10 15 20 0 5 10 15 20 Cycle Index Cycle Index Self et al., Chemistry of Materials, Under Review Substitution of Mo into NMC structure decreases 13 electrochemical capacity but improves cycling stability. Technical Accomplishment As an alternative to Cr substituted Li2MoO3 cathode (part of milestone-2) Cr-doped NMC and MoO3-coated NMC cathodes were synthesized and characterized. All materials were phase-pure with layered R3തm structure (XRD data not shown)

MoO3-Coated NMC111 2.0-4.5V Cycling Performance vs. NMC

Negligible Mo redox activity

LiNi0.317Mn0.317Co0.317Cr0.05O2

• MoO3 coating and Cr-doping had no effect on the initial reversible capacity, but both materials showed accelerated capacity fade relative to baseline NMC • Ni/Mn/Co 3+/4+ are main redox centers in all materials • Ongoing work is focused on optimizing doping and coating levels to improve cycling performance

14 Self et al., Unpublished 2018 Response to Reviewers Comments

Reviewer # 2 The cyclic stability of Li2CuxNi1-xO2 has been marginally improved as shown in previous report, but the (low) voltage profile and low capacity are not attractive. Further, fairly good efforts were made

in synthesizing and characterizing the molybdenum analogue of Li2MnO3 with greater oxygen stability through electrochemistry, XRD, and Raman. Response : We agree with reviewer’s comment. Li2CuxNi1-xO2 in our case was used as model system for demonstrating lattice oxygen loss at ~ 4V not mediated by any carbonate electrolytes. This effectively demonstrated the irreversible anion redox participation with substantial loss of electronegativity of oxygen.

Reviewer # 3 This project studied interesting oxide compounds of Li-rich Li2MO3 and Li2MO2. However, the reviewer could not see what merits these types of oxides have in developing high energy cathode materials. Response : We agree with reviewer’s observation and in FY18 we have refocused our effort on Mo and Cr doping in NMC and molybdenum based composite cathodes as part of our strategy to stabilize oxygen loss at high voltage.

Reviewer # 4 Li2MoO3 may not be the right material due to its low capacity and conversion to amorphous state after the first cycle. Response : We clearly stated earlier that Li2MoO3 is studied in the context of using this as a structural unit for stabilizing the layered NMC cathode system. As part of FY 18 deliverable

we have provided results on the first composite cathode system x.Li2MoO3•(1-x)LiMO2

15 Collaborations and Coordination with other Institutions

Electron Microscopy Drs. Chongmin Wang & Pengfei Yan

In-operando X-ray Synchrotron Studies and Microscopy Dr. Feng Wang

Synchrotron X-ray microscopy and 3D microstructure Dr. Johanna Nelson Weker

Modeling and oxygen activity of Li-excess compositions

16 Remaining Barriers and Challenges

• Determine if anionic substitution like fluorination can suppress oxygen evolution and enable high voltage operation. • Investigate oxygen stability in Li-excess cation disordered cathodes. • Determine the stability of cathode powders or electrodes in air, especially with respect to Li2CO3 formation on surface. • Optimize the synthesis and electrochemical performance of cation disordered Li- excess compositions: Li2MoO3 and Li-excess Cr-substituted LiMoO2. • Develop approaches to mitigate lattice oxygen loss and improve structural stability of the cathode surface.

17 Any proposed future work is subject to change based on funding levels Proposed Future Research 1. We will continue our emphasis on synthesis and optimization of lithium-excess cation disordered oxides having rock salt and layered composition. Specific approaches include substitution of earlier TM elements such as Mo, Cr, and Ti. A few promising high capacity (and voltage) compositions include but are not limited to Li1+xMoyCr1-x-yO2; Li1+xNbyMn1-x-yO2 ; Li1+xNbyV1-x-yO2 ; Li1.2Mn0.4Ti0.4O2. 2. As part of the cathode design and optimization process we will combine various spectroscopic, microscopic, and structural probes for the disordered cathode compositions to (i) understand the role of cation disorder/mixing for enhancing lithium diffusion pathways, (ii) contribution of oxygen redox participation and its reversibility and (iii) unique bonding and electronic structure that contributes to the extra capacity. 3. Undertake both anionic and cationic co-doping to stabilize the high capacity disordered cathodes. For example, simultaneous Mo or Nb and F substitution in Li1+xMO2 M = Mn, Ni Neutron Diffraction Raman Mapping

Disordered Li-Excess Cathode

Mass Spectrometry 18 18 Image used with permission from: Lee et al. Science, 2014, 343, 519. Technical Approach: Summary (003) Synthesis and in-depth analysis of lithium-excess and multi- lithium chemistries for high voltage, high capacity cathodes - Model driven synthetic approaches: solution-based,

sol-gel and solid state methods. Discharge - Diagnostic tools include a suite of microscopic, spectroscopic, and analytical techniques. - Emphasis is placed on understanding and preventing Charge 3.2 3.4 3.6 3.8 oxygen loss at high voltage 2θ / deg. (λ = 0.2953 Å) Accomplishments:

- Identified chemical and structural changes that occur in Li2MoO3 cathodes during electrochemical cycling

- Unraveled mechanisms of electrochemical activity and degradation of Li2MoO3 cathodes using a combination of X-ray and neutron diffraction, Raman spectroscopy, electrochemistry, gas evolution experiments, and TEM. - Developed synthesis routes to produce composite NMC-based cathodes containing a

Li2MoO3 structural stabilizing unit Ongoing work: - Optimize the synthesis and processing of cation disordered Li-excess compositions. - Investigate oxygen stability in disordered cathodes and continue to develop approaches to prevent oxygen loss.

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